1. Field of the Invention
The present invention relates to a motor and, more particularly, to a motor having a stator that can be reliably positioned.
2. Description of the Related Art
A conventional motor generally includes a base, a stator, and a rotor. The base includes a shaft tube around which the stator is mounted. The rotor is rotatably coupled to the shaft tube. The stator generates an alternating magnetic field to drive the rotor to rotate.
The stator and the shaft tube are generally fixed together by press fitting or gluing. However, the stator is apt to disengage from the shaft tube if the stator is engaged with the shaft tube by press fitting. On the other hand, if the stator is fixed to the shaft tube by gluing, factors including the amount of the glue, the curing time of the glue, etc. must be considered, leading to inconvenience to assembly. Furthermore, if it is intended to miniaturize the motor, the axial height of the stator must be reduced (such as by reducing the number or the thickness of the silicon steel plates of the stator), leading to a decrease in the engaging area between the stator and the shaft tube. The stator is more likely to disengage from the shaft tube if press fitting is utilized.
FIG. 1 shows a conventional motor 8 including a shaft tube 81, a stator 82, and a rotor 83. A plurality of first engaging portions 811 is provided on a top end of the shaft tube 81. The stator 82 includes a lining 821, with a plurality of second engaging portions 822 formed on a periphery of a central opening of the lining 821. The first and second engaging portions 811 and 822 are fixed together by heat fusion. Thus, the stator 82 can reliably be fixed to the shaft tube 81 by the heat fusion structure formed by the first and second engaging portions 811 and 822. An example of such a structure is disclosed in Taiwan Utility Model No. M419336.
Although the motor 8 can provide the stator 82 with an enhanced positioning effect by using the first and second engaging portions 811 and 822, the first engaging portion 811 of the shaft tube 81 and the second engaging portion 822 of the lining 821 of the stator 82 do not extend to the opening of the top end of the shaft tube 81. Namely, the motor 8 can not provide advantages, such as directly closing the opening of the top end of the shaft tube 81 by the stator 82 (for providing anti-dust function or maintaining lubrication oil), pressing against members mounted in the shaft tube 81 (for positioning purposes), and retaining the rotor 83 (for the purposes of preventing disengagement). As an example, an oil seal 84 or the like is required to maintain the lubrication oil. However, the oil maintaining effect of the oil seal 84 mounted in the shaft tube 81 is not satisfactory. Furthermore, the oil seal 84 complicates the structure and reduces the assembling convenience.
FIG. 2 shows another conventional motor 9 including a base 91, a rotor 92, and a stator 93. The base 91 includes a shaft tube 911, with the rotor 92 rotatably coupled to the shaft tube 911. The stator 93 is mounted around the shaft tube 911 and includes an insulating bobbin 931 having a restraining member 932. The restraining member 932 extends to an opening of the top end of the shaft tube 911. The restraining member 932 retains members received in the shaft tube 911 and retains the rotor 92, preventing disengagement of the rotor 92. An example of such a motor is disclosed in Taiwan Patent Publication No. 200952307.
Compared to the conventional motor 8 of FIG. 1, the conventional motor 9 provides some advantages, including directly pressing the members in the shaft tube 911 by the stator 93 and retaining the rotor 92. However, the stator 93 providing the above advantages can only be mounted to the outer periphery the shaft tube 911 by fashions such as press fitting, leading to a poor positioning effect between the stator 93 and the shaft tube 911 as well as the risks of disengagement of the stator 93 due to heat expansion and cold shrinkage. Furthermore, if it is intended to miniaturize the motor 9, the stator 93 is apt to disengage from the shaft tube 911 if the stator 93 is mounted by press fitting. Thus, a novel structure for reliably fixing the stator 93 is required.